by Meagan Fitzgerald, Laurie Cipriano and John Bacon, USA TODAY

by Meagan Fitzgerald, Laurie Cipriano and John Bacon, USA TODAY

ARAPAHOE COUNTY, Colo. - School district administrators were allowed back into Arapahoe High School on Monday after investigators finished processing the scene where a gunman shot a fellow student at point-blank range before killing himself Friday.

Arapahoe County Sheriff Grayson Robinson said in a statement Monday that investigators finished their work over the weekend and gathered the evidence they needed.

Crime scene investigators included the sheriff's office, the Colorado Bureau of Investigation and the Federal Bureau of Investigation.

Authorities said Karl Pierson, 18, shot Claire Davis on Friday before killing himself as the result of an apparent dispute with a school staff member.

School was canceled Monday and the Littleton Public Schools district has not said when classes will resume.

A stunned community held a prayer vigil Sunday in support of Claire, 17, who was clinging to life in a coma. The horse lover, babysitter and "great student" remained in critical condition at Littleton Adventist Hospital.

Colorado Gov. John Hickenlooper, who asked the nation to pray for Claire, credited security procedures adopted after the 1999 massacre at nearby Columbine High School for helping put a quick end to the shooting.

"We all have to keep Claire in our thoughts and prayers," Hickenlooper said Sunday on CBS' Face the Nation.

Claire's parents "are remarkable people. I feel so directly their suffering. ... They raised this beautiful young woman who had her whole life ahead of her," Hickenlooper said.

August Clary, a classmate and friend, said horsemanship is a big part of Claire's life. She spends long hours training her horse, Graphite, August said.

"A very sweet girl. She's really smart, really bright," said August, who has known Claire since freshman year. He had government class with her Friday morning. "She wouldn't hurt a fly. She's just a really great girl, and we hope she's gonna be OK."

On Saturday, Sheriff Robinson called Davis "a young woman of principle. She is a young woman of purpose. ... She was an innocent victim of an evil act of violence."

Robinson said Pierson entered the school armed with a shotgun he bought legally, rounds of ammunition strapped across his body, a machete and a backpack with three Molotov cocktails.

Pierson, in less than two minutes, fired five shots and ignited one of the Molotov cocktails before running to the back of the school library and killing himself, Robinson said. Robinson credited the quick response of a sheriff's deputy assigned to the school with stopping a mass murder.

"The shooter knew the deputy was in the area," Robinson said at a news briefing. "We believe that the response ... was absolutely critical to the fact that we did not have additional injury or deaths."

Tracy Murphy, a librarian and debate team coach, was believed to have been the gunman's target. Pierson was unable to find Murphy, who coached Pierson and had disciplined him in September. Robinson said Claire's shooting appeared to be random.

Hundreds of students, parents and community members filled a local park Saturday night for a candlelight ceremony, expressing shock and pain at the tragedy that unfolded at the Centennial school.

Pierson was "a funny kid," August said. "He's smart. He's in the Eagle Scouts, a very intelligent kid. Did not like being wrong. If you're arguing with him ... that's a feat if you win an argument against him."

"It didn't feel real until you see everybody" at the vigil, said Summer Skrzypek. "She was a good friend and was always there if you needed her."

Students sang the school fight song and reminded each other that "Warriors" stick together. They shouted out words of encouragement, held a moment of silence and prayed.

The Davis family issued a statement Saturday saying Claire "has severe head trauma as a result of a gunshot. She needs your continued prayers."